Sonar transducers are ideally designed for specific system needs such as beamwidth, useful range, impedance, and bandwidth. These designs are often revised based on the practical limits of available power, physical space, acoustic cavitation, thermal limits, mechanical stress, electrical stress and others. However, sometimes sonars are designed around existing legacy or low-cost hardware.
A specific example from the commercial marine industry is a piezoelectric transducer disk made of ceramic to produce sonar waves. These devices can provide dual sonar frequencies, relying on a lateral (radial) vibration mode for ˜70-80 kHz and a thickness vibration mode for ˜200 kHz. The thickness mode directly radiates sound, whereas the radial mode mechanically couples vibrations, in a Poisson sense, into a quasi-thickness direction, which in turn also radiates sound. This is one example, therefore, where a single transducer may be designed to produce two output frequencies, thus avoiding the expense of a second transducer.
In the commercial marine example, the −3 dB main-lobe beamwidth of the acoustic vibration beam produced at each frequency is primarily determined by the ratio of the acoustic wavelength and the outer diameter of the piezoelectric ceramic. The power input and output of such transducers is primarily limited by the volume of the piezoelectric ceramic, because such materials have a limited allowed energy density before a mechanical, thermal, electrical or combined failure occurs. For this specific example, the electrical driving power input limit is approximately 1.8 kW for a commonly used 25-mm-diameter by 9.5-mm-thick lead zirconate titanate (PZT) ceramic, and the beamwidths are typically 40 and 14 degrees, respectively, for ˜75 kHz (lateral mode) and ˜200 kHz (thickness mode) operation.